In addition to "chicken little," Janice Jaquith's self-description of her essay ["Forget birds: We could all die from this flu," March 3], your readers might also be interested in hearing from a voice in the wilderness on the threat of the global bird flu pandemic.

Dr. Paul W. Ewald, author of two influential books on infectious disease, thinks it is unlikely that bird flu (H5N1) will become a 1917-style death-flu plague.

According to Dr. Ewald, the kinds of evolutionary pressures that helped create the 1917 pandemic are not currently in play. In 1917, trench-warfare conditions, which provided large numbers of sick and wounded immobile hosts for the virus, generated the natural selective pressure that helped the bug evolve extreme virulence. (New York Times health science reporter Gina Kolata believes the death toll may have been as high as 100 million.)

Because no such conditions currently exist in Viet Nam, the bird flu epicenter, the disease likely to emerge may turn out to be nasty, but not lethal.

Since the late 1970s, WHO officials have been warning of the imminent recurrence of a 1917-style flu plague, but Ewald has consistently counter-argued that such warnings are unfounded as long as evolutionary pressures favoring virulence are not at work. So far Ewald has been right.

Ewald is part of a revolutionary movement in medicine that approaches health threats from the perspective of evolutionary biology. If the evidence supports this approach, then our understanding of not only viruses such as the flu but also big killers such as heart disease and cancer may have to undergo radical change. Solutions will likely involve bolstering the immune system, which has evolved over the eons to help us deal with disease organisms.

Tinkering with minute chemical factors, the basis of modern pharmacological medicine, is unlikely to contain the evolution of infectious disease. So if you want to be prepared for disease in general, find ways to strengthen immunity.